The present invention relates to a hybrid navigation system including an electromagnetic wave navigation receiving apparatus and geomagnetic sensor especially but not exclusively installed in an automotive vehicle, and more particularly relates to the hybrid navigation system for determining a relative position and direction of the vehicle and method therefor in which an intensity of magnetization on a vehicle body is calculated and which compensate for an erroneous determination of the relative position and direction thereof.
In general, a magnetization often occurs on a vehicle body when the vehicle runs on a road. To determine continuously the relative position and direction to, e.g., a destination of the vehicle, the hybrid navigation system uses a GPS (Global Positioning System) receiving apparatus and a geomagnetic sensor. However, when the vehicle runs on a road, the magnetization affects the detection result of the geomagnetic sensor so that an accurate measurement of the relative position and direction of the vehicle cannot be achieved.
To cope with such a problem described above, a technique for correcting an output of the geomagnetic sensor for compensating for the magnetization of the vehicle body has conventionally been proposed.
A Japanese Patent Application First Publication No. (Tokkai) Sho 58-48811 published on Mar. 22, 1983 exemplifies such a technique as described above.
In the above-identified Japanese Patent document, the correction technique is such that with a turn of the vehicle through 360.degree., center point coordinates of an output data of the geomagnetic sensor is detected and an effect of the intensity of magnetization of the vehicle body on the output of the geomagnetic sensor is eliminated.
In the conventional technique on the correction for the magnetization of the vehicle body, however, the correction of the directional data derived from the geomagnetic sensor cannot be carried out without sampling of the directional data of the vehicle during one circular turn of the vehicle. In addition, to take a sampling of the directional data during one circular turn of the vehicle, a considerable time and distance may be required from the start of the sampling to the end of the sampling when the vehicle runs. Therefore, if a magnetization state on the vehicle body changes during the sampling operation, an erroneous correction has resulted.
Furthermore, since the correction based on the direction data derived by the circular turn sampling is carried out in such a way that data not falling in a usually expected data limit are delted to reduce an error of the correction value due to external disturbances, the correction cannot be made any more if a large change occurs in the magnetized state of the vehicle body.